Imagers typically have an array of pixels containing photosensors, where each pixel produces a signal corresponding to the intensity of light impinging on that element when an image is focused on the pixel array. The signals may then be digitized and stored, for example, for subsequent display of a corresponding image on a monitor, or for providing hardcopy images, or for providing information about the captured image.
When capturing a color image photosensors must be able to separately detect color components of the captured image. One of the most challenging problems in color image processing is adjusting the color gains of the system to compensate for the variations in the illumination spectra incident on the imager due to the illumination source, also known as white balance. For example, when a digital camera is moved from outdoors (sunlight) to indoor fluorescent or incandescent light conditions, the color in the image may shift. If an image of a white card looks white when indoors, for example, it might look bluish outside. If it looks white under fluorescent light, it might look yellowish under an incandescent lamp.
In order to compensate for changes in illumination spectra, the gains of the color processing systems and/or imager should be adjusted, using for example, automatic white balance techniques. Automatic white balance relies on accurately measuring the color pixels of the image. During manufacturing, color characteristics of imagers may vary substantially. An imager with color characteristics that are substantially different from those that the automatic white balance assumes may result in a malfunction of the automatic white balance.
Accordingly, there is a need and desire for methods, systems and apparatuses for calibrating imagers to provide an improved automatic white balance function.